A continuous mixing reactor is a reaction vessel that has a continuous mixer having internal circulation, wherein circulation is provided by an impeller. The reactor is a horizontal pressure vessel having an outer shell, an inner circulation tube, a mixing impeller, and an indirect heat exchange provided by a tube bundle. These reactors are suitable for carrying out chemical reactions under conditions providing intimate contact between reactants, in a single phase or in multiple phases. Continuous mixing reactors are known, and examples can be found as described in U.S. Pat. Nos. 3,759,318 and 3,965,975.
Basic operation of a continuous mixing reactor includes:    1. The continuous mixing reactor shell serves to contain the reaction mixture.    2. The circulation tube serves to establish an internal flow path in the reactor (down the center of the circulation tube and through an annular passage which exists between the circulation tube and the shell).    3. The shell has a hydraulic head, which contains shaft sealing means and any required bearings for the impeller shaft. The hydraulic head also incorporates a reversal zone for flow of fluid from the impeller.    4. The impeller effects mixing and circulation in the reactor. A mixing circulating impeller provides high shear and turbulence to reactants to maximize rate.    5. Indirect heat exchanging means provided as a tube bundle containing a heat exchanging medium for addition or removal of heat absorbed or generated during the reaction. Temperature control is achieved by addition or removal of reaction heat by heat exchange throughout a reaction zone in the reactor. Tube bundles may be of the U-tube type, bayonet tube or others.
The conventional flow path within a continuous mixing reactor, starting from the discharge side of the impeller, is through a reversal area in a hydraulic head, thereafter through an annular passage between the circulation tube and the outer shell, at the end of the circulation tube through a reversal area in the end of the reactor opposite the impeller, and finally through the center of the tube bundle, that is, the central section of the reactor, within the circulation tube back to the impeller. Reactants are normally fed as near as possible to the eye of the impeller so that they are immediately and thoroughly mixed and dispersed into the main body of the reaction mix.
The design of a continuous mixing reactor is to maximize circulation and turbulence of the internal fluids.
An example of a process performed in a continuous mixing reactor is alkylation. In an alkylation process light olefins (such as propylene, butylenes, amylenes) are reacted with an isoparaffin (branched alkane), such as isobutane, in the presence of an acid catalyst such as sulfuric acid, to form an alkylate product. The alkylate product is a mixture of gasoline boiling range branched hydrocarbons, which can be blended with a refinery gasoline pool, to increase the gasoline octane and reduce the vapor pressure.
In an alkylation process, olefin and isoparaffin are combined in a feed, which is injected into a suction side of the impeller inside the circulation tube. The impeller rapidly disperses the feed within the acid catalyst to form an emulsion. The emulsion is circulated by the impeller at high rates within the reactor.
Tube wear has been found in continuous mixing reactors having conventional flow paths at the reversal area in the end of the reactor opposite the impeller. In an alkylation process, wear may be due to corrosivity of acid catalyst, temperature and other factors. Flow distribution in the reversal area creates pressure losses resulting in uneven flow to the center of the bundle.
It is desired to reduce and minimize tube wear of tubes in tube bundle heat exchanging means. For example reduce and minimize wear at the end of the circulation tube in a continuous mixing reactor, to more efficiently use the heat exchange capacity of the tube bundle and to provide better flow distribution in the tube bundle. The continuous mixing reactor and method disclosed herein meets these needs.